linux-kernel - Re: [PATCH bpf-next v3 12/14] bpf: Pull tools/build/feature biz into selftests Makefile

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Date:   Fri, 4 Dec 2020 11:00:24 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Brendan Jackman <jackmanb@...gle.com>
Cc:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Yonghong Song <yhs@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        KP Singh <kpsingh@...omium.org>,
        Florent Revest <revest@...omium.org>,
        open list <linux-kernel@...r.kernel.org>,
        Jann Horn <jannh@...gle.com>
Subject: Re: [PATCH bpf-next v3 12/14] bpf: Pull tools/build/feature biz into
 selftests Makefile

On Fri, Dec 4, 2020 at 1:41 AM Brendan Jackman <jackmanb@...gle.com> wrote:
>
> On Thu, Dec 03, 2020 at 01:01:27PM -0800, Andrii Nakryiko wrote:
> > On Thu, Dec 3, 2020 at 8:07 AM Brendan Jackman <jackmanb@...gle.com> wrote:
> > >
> > > This is somewhat cargo-culted from the libbpf build. It will be used
> > > in a subsequent patch to query for Clang BPF atomics support.
> > >
> > > Change-Id: I9318a1702170eb752acced35acbb33f45126c44c
> >
> > Haven't seen this before. What's this Change-Id business?
>
> Argh, apologies. Looks like it's time for me to adopt a less error-prone
> workflow for sending patches.
>
> (This is noise from Gerrit, which we sometimes use for internal reviews)
>
> > > Signed-off-by: Brendan Jackman <jackmanb@...gle.com>
> > > ---
> > >  tools/testing/selftests/bpf/.gitignore |  1 +
> > >  tools/testing/selftests/bpf/Makefile   | 38 ++++++++++++++++++++++++++
> > >  2 files changed, 39 insertions(+)
> >
> > All this just to detect the support for clang atomics?... Let's not
> > pull in the entire feature-detection framework unnecessarily,
> > selftests Makefile is complicated enough without that.
>
> Then the test build would break for people who haven't updated Clang.
> Is that acceptable?
>
> I'm aware of cases where you need to be on a pretty fresh Clang for
> tests to _pass_ so maybe it's fine.

I didn't mean to drop any detection of this new feature. I just didn't
want a new dependency on tools' feature probing framework. See
IS_LITTLE_ENDIAN and get_sys_includes, we already have various feature
detection-like stuff in there. So we can do this with a one-liner. I
just want to keep it simple. Thanks.